the nervous system

the nervous system is divided into 2 parts

central nervous system (CNS)

• brain

• spine

peripheral nervous system (PNS)

• somatic nervous system

• autonomic nervous system

somatic nervous system

which carries messages between the muscles and sense organs to and from the CNS allowing us to sense and interact with our environment

autonomic nervous system

which regulates the body’s vital functions automatically and involuntarily. Controls heartbeat, digestion, breathing, and circulation

sympathetic vs. parasympathetic nervous system

• Sympathetic system get activated in response to the environment; prepares for optimal responses to stimuli.

• Parasympathetic system “rests and digests” and returns the body to it’s non-arousal state deactivating the sympathetic response. Both systems work involuntarily

what is the parasympathetic system responsible for?

• Responsible for emotions – emotions occurring at incorrect moments are often a source of psychological disorders. E.g. Anxiety, Panic, Depression, Mania.

• Any disorder based on disconnection between bodily or emotional state and the environment

neuron definition

nerve cells that run through the body and communicate with each other

basic neuron types

• bipolar (interneuron)

• unipolar (sensory neuron)

• multipolar (motoneuron)

• pyrimidal cell

parts of the neuron

neuroplasticity definition

the brain has the ability to reorganize itself by altering connections between neurons to adjust to changes in the environment, injury or disease

synapse definition

the junction between the axon terminals of one neuron and the dendrites of another

sensory neuron definition

carries information received by the senses to the CNS

motor neuron definition

carry messages from the CNS to the muscles and glands and influence their functioning

spinal reflex definition

a body’s automatic response to a trigger without the involvement of the cortex

the neural impulse

Neurons fire when triggered by:

• The presence of a critical amount of key chemicals emitted by neighbouring neurons

• The stimulation of an attached specialized structure by input from the environment.

• Firing consists of a directional impulse – action potential

• Moves at 200mph

the electrochemical signal

The signal that travels the length of the neuron is actually a change in the polarity of the outside of the axon.

• The resting charge on the cell is -70 millivolts.

• This charge is created by a membrane around the cell that keeps positively charged sodium ions (Na+) on the outside of the cell and positively charged potassium ions (K+) in the inside – selectively permeable

impulse

Once the threshold is achieved in the cell body, the protein “gates” of the axon open and Na+ ions rush in.

• For 1 millisecond, the outside of the axon body becomes – and the interior becomes +

all or none response

Once the impulse is triggered, the intensity of the signal is constant

• All or None Law–the stimulus does not provide the energy of the nervous impulse. A neuron’s reaction is either firing or not firing

• This means that a stronger sensation is caused by a greater number of neurons being stimulated, not a stronger impulse

synaptic transmission

Scientists had always believed that there was some mechanism connecting two neurons together.

• This was finally proven in 1920 by Otto Loewi

• Lowei’s experiment proved that the transmission from one neuron to the next involved a chemical substance

synaptic transmission (2)

As the impulse reaches the axon terminals, tiny sacs of specialized proteins called synaptic vesicles rupture at the surface of the terminal

• These vesicles pop and release a chemical into the synapse called a neurotransmitter

neurotransmitters definition

chemical messengers that travel across the synaptic gap and have an excitory or inhibitory effect on the adjacent neuron

receptors

CNS (brain, spine) and PNS (somatic, autonomic).

neurotransmitters

There are over 100 different identified

• 2 types – must be in balance for optimal functioning

• Excitatory – facilitate impulse crossing the synapse

• Inhibitory – stop the impulse from crossing the synapse

agonists & antagonists

Agonists – chemicals that enhance the action of a neurotransmitter eg SSRIs

• Antagonists – chemicals that counteract a neurotransmitter eg GABA

• The interaction of all these classes of neurotransmitter make simple cause and effect links between a chemical and a behaviour difficult

lock & key model

Each neurotransmitter is paired with the special receptor at the end of the post-synaptic neuron.

• Each receptor can only be activated by it’s paired neurotransmitter

reuptake, oxidation, & drift

Excess neurotransmitter in the synapse is removed to lower neurotransmitter levels to a sub-critical level to prevent prolonged stimulus or interference in several ways:

• The axon terminal will reabsorb excess back into the neuron cell.

• Enzymes break down excess neurotransmitter rendering them unable to bond with receptors and affect receiving neurons